Philipp wenzel



(No Model.) P. WENZEL.

ENAMELED SLATE.

No. 333,573. Patented Jan. 5, 1333.

' I Jmrenfur: MM i245; QZWM,

UNITED STATES PATENT OFFICE,

PHILIPP WENZEL, OF MENTZ, GERMANY.

ENAMELED SLATE.

SPECIFICATION forming part of Letters Patent No. 333,578, dated January5, 1886. Application filed April 29, 1885. Serial No. 163,993. (Nomodel.) Patented in Germany October 7, 1884, No. 29,267.

To all whom it may concern.-

Be it known that I, PHILIPP WENZEL, a citizen of the German Empire,residing at Mentz, Germany, have invented certain new and usefulImprovements in Slates, of which the following is a specification.

My invention relates to writing-slates, and has for its object toproduce an improved writing-slate having a white surface upon apractically indestructible base that shall be cheap, durable, andpracticable; and to these ends my invention consists in a sheet metalcoated or covered with enamel on one or both sides, the enamel beingproperly prepared to receive the marks from an ordinary black or otherlead pencil.

It has been found that a slate with a white surface upon which black orother colored lines can be easily and accurately drawn is a greatdesideratum, being much better for the eyes than a black or dark slateupon which white lines or marks must be made. Moreover, a slate having apractically indestructible body or base, if properly made, has manyadvantages over the slates in common use. Many attempts have been madeto overcome these objections and to produce a practically indestructibleslate having a white writingsurface, as by covering a sheet of tin withwhite paint; but these have been found to lack the quality ofdurability, as well as failing to properly receive the marks madethereon, and to allow of their erasure without injuring the surface ofthe slate. White slates 3 5 have also been made of glass, porcelain,marble, and the like; but these are expensive and easily destroyed.Paper and wooden slates have been made in a variety of colors byapplying paints or coloring-matter thereto, and it has been proposed tomake slates of celluloid plates treated with emery-powder andreenforced; but these have not proved efficient or durable, as themoisture generally used to erase the marks thereon speedily injures ordestroys the body of the slate.

The object of my invention is to overcome all these difficulties, and Iaccomplish this object by constructing slates in a manner moreparticularlypointed out hereinafter.

I use a metallic base of some sheet metal, preferably iron, and this maybe quite thin, and

consequently cheap. The surfaces of the sheet metal are first thoroughlycleaned and an'enamel applied thereto in any convenient manner, as bymixing the enamel-powder in the form of a paste, which is spread overthe surfaces of the metal plate and allowed to dry. The enamel may be ofvarious kinds; but to produce a fine clear white surface I find that anenamel composed, essentially, of silicious materials having somemetallic oxides or earths mixed therewith are cheap, durable, andpracticable. The enamel having been properly applied to the surfaces ofthe metal base, it is placed into a suitable muffle-furnace wherein thetemperature is raised to such a degree that the enamel melts and forms athin even coating all over the plate, and at the same time it adheresclosely to the plate, so that it is not liable to crack or peel off orotherwise become uneven. Upon removing the plate from the muffle-furnaceand cooling the same, the enameled surface is found to be too smooth toproperly take the lead or other substance from the pencil and to receiveand retain the marks, and to properly prepare the surface for thatpurpose I remove the exterior glaze or surface of the enamel, or roughenor mat the same by immersing it in a bath of some proper acidashydrofluoric or equivalent aci(l-acting destructively upon the enamel,where it remains a sufficient time to allow the acid to bite theenameled or glazed surface to produce the desired toothed or mattedcondition to best receive and retain the marks. In some cases thiscondition of the surface may be produced by abrasion, as by asand'blast; but I have found the acid bath most convenient andsatisfactory. The surfaces having been properly prepared, the materialmay be cut to any desired size or shape and framed in any of thewell-known ways. In this way I am enabled to produce a slate having awhite surface on a very thin metallic base, that is light, cheap, andpractically indestructible, and one on which the ordinary black-leadpencils may be freely and conveniently used to produce good, sound, andunbroken black or colored lines, and these lines may be easily andthoroughly erased without leaving any traces on the surface or injury tothe enamel.

In the accompanying drawing, forming a part of this specification, Ihave shown a representation of my invention as embodied in a slatehaving a frame of ordinary shape and construction, the surface of theslate being white with black lines thereon.

It is understood that the sheet metal may be covered or coated with theenamel surface on one or both sides, as desired.

I do not desire to limit myself to the precise details set forth above,as they may be varied without departing from the spirit of my invention.

I have used the word white as applied to the color of the slate in arelative sense, as compared with the dark mark of the pencil.

What I claim as my invention is 1. A Writing slate consisting of a metalbody coated or covered with enamel and having a white surface,substantially as described.

PHILIPP XVENZEL. [L. s]

W'itnesses:

J on. A. Hone, J os. Scorr.

